Scheduling delivery of upstream traffic based on downstream traffic in optical networks

ABSTRACT

In general, techniques are described for monitoring downstream traffic in order to schedule delivery of upstream traffic in a computer network. The techniques may be implemented by an optical line terminal (OLT) comprising a control unit and an interface. The control unit determines an amount of upstream data that is waiting at one of a plurality of ONTs to be transmitted upstream to the OLT, and determines an amount of downstream data that is transmitted by the OLT to this ONT. The control unit increases the determined amount of upstream data based on the determined amount of downstream data transmitted by the OLT to the ONTs and, after increasing the determined amount of upstream data, generates an upstream grant map that grants time slots to the ONTs based on the determined amount of upstream data. The interface transmits the upstream grant map downstream to the ONTs.

TECHNICAL FIELD

The disclosure relates to electronic scheduling of upstream traffic frommultiple network devices on a shared telecommunication medium.

BACKGROUND

An optical network, such as a passive optical network (PON) as anexample, often delivers voice, video and/or other data among multiplenetwork nodes. In the case of a PON, the network nodes are oftenreferred to as optical network terminals (ONTs). The PON can deliverdata among multiple ONTs using a common optical fiber link. Passiveoptical splitters and combiners enable multiple ONTs to share theoptical fiber link. An optical line terminal (OLT) transmits informationdownstream to the ONTs, and receives information transmitted upstreamfrom the ONTs. Each ONT terminates the optical fiber link for aresidential or business subscriber, and is sometimes referred to as asubscriber or customer premises node.

Each ONT is connected to one or more customer premises equipment (CPE)devices, which ultimately receive the voice, video and other datadelivered via the PON. Examples of CPE devices include computers,telephones, television set-top boxes or the like. An ONT on a PON mayreceive traffic from several sources. Some sources may be commonly usedamong several ONTs on a PON. For example, several ONTs may access acommon traffic flow associated with switched digital video (SDV) orother multicast streams. Other sources may produce traffic flows thatare unique to an individual ONT. For example, an individual ONT mayreceive web content from an Internet service provider (ISP) or voicedata from the public switched telephone network (PSTN).

To schedule delivery of data, such as requests for data stored on aserver located in a public network, upstream from ONTs to OLTs over theshared or common optical fiber link, the OLT maintains a scheduler thatgrants each of the ONTs to which it connects (or, more specifically,so-called traffic containers or “T-conts” storing packets within each ofthe ONTs) a time slot during which each of the ONTs may transmit theirrespective upstream data to the OLT. In order to schedule these grants,the OLT may determine how much data each of the ONTs has to transmitupstream. In some instances, the OLT may issue a request to the ONTs fora report of how much data is stored to each of its one or more upstreamqueues. Those ONTs that support this form of status reporting mayrespond with an approximate amount of how much data is stored to theseone or more upstream queues. For those ONTs that do not support statusreporting, the OLT may grant each of these ONTs a set amount of time totransmit upstream and then monitor the amount of traffic sent upstreamby these ONTs during their granted set amounts of time. However, inmonitoring upstream traffic, the OLT may not proactively schedule timeslots to accommodate the upstream data waiting at the monitored ONTs.Instead, the OLT may react to the data sent upstream by these ONTs thatdo not support status reporting. In this reactive mode, the OLT may failto schedule an adequate number of time slots to accommodate the amountof data waiting to be sent upstream by the monitored ONTs, which mayhamper network operation in certain instances.

In any event, based on the reported status and/or the monitored status,the OLT may determine an upstream grant map that grants each of theseONTs one or more time slots during which these ONTs may transmitupstream data to the OLT. The OLT may generate this upstream grant mapin a manner that accommodates different levels of service and pastdelivery of service using, for example, a weighted round robin orweighted fair queueing algorithm. Typically, the OLT determines thisupstream grant map after each scheduling round, which is typically a setperiod of time during which the OLT may receive status reports from orafter determining a monitored amount of data to be transmitted by theONTs. The OLT determines this grant map at the end of each schedulinground as the OLT may not otherwise have enough information to scheduletime slots appropriately for each of the ONTs. The period of time duringwhich the OLT has to determine this grant map after receiving the statusreports during any given scheduling round and monitoring upstream databefore the grant map has to be sent downstream to the ONTs is, forexample, approximately 125 micro seconds (μs) in a gigabit PON (GPON).Considering that the OLT also takes into consideration different levelsof service and past delivery of service, computing this grant map inthis limited amount of time may require significant resources in termsof processing power and storage capacity.

SUMMARY

In general, this disclosure describes techniques that provide a grantscheduler for an OLT that may pre-compute certain aspects required todetermine the upstream grant map so as to reduce the requirements forprocessing power and storage capacity in comparison to conventionalimplementations. In accordance with these techniques, the OLT mayconvert upstream data amounts either reported bystatus-reporting-enabled ONTs or monitored by the OLT into grant cyclespending (GCPs) without waiting to receive all of the other statusreports and/or determine the monitored data amounts for those ONTs thatdo not support status reporting. By pre-computing the GCPs as theseupstream data amounts are received and/or determined, the OLT may reducethe number of computations that need be performed that are tangentiallyunrelated to generating the grant map, such as converting upstream dataamounts to time slots, during the grant map generation period of timebetween receiving status reports or monitoring the last ONT and sendingthe upstream grant map downstream to the ONTs (which is commonly a timeperiod of approximately 125 μs, as noted above).

By removing at least partially the conversion of data amounts into timeslots through the conversion of data amounts into GCPs before the grantmap generation time period, the OLT may then perform more computationsduring the grant map generation time period that may be considered moredirectly related to actual grant map generation, such as allocating timeslots for ONTs based on the GCPs. In this manner, the techniques mayenable the OLT to perform more iterations allocating time slots to ONTsduring the grant map generation time period, which may result in betterscheduling results as measured in terms of fair bandwidth allocationwhile also reducing burst sizes and latency considering that morebandwidth may be scheduled in comparison to conventional systems thatboth convert data amounts into time slots and allocate time slots duringthe grant map generation time period.

Moreover, techniques are described to better monitor those ONTs that donot support status reporting so as to improve OLT scheduling ofmonitored ONTs. These monitoring techniques may involve monitoringtraffic sent downstream to these monitored ONTs. In response todetecting a marked increase in bandwidth usage by one of these monitoredONTs, the OLT then, in accordance with the techniques, allocates one ormore additional grant cycles pending to that monitored ONT proactively,thereby improving grant response times in certain instances. Theallocation of the number of additional grant cycles pending may be basedon the extent of the increase in downstream bandwidth usage. While thesetechniques may be most beneficial for allocating upstream bandwidth tothose ONTs that do not support status reporting, the techniques may alsobe applied with respect to those ONTs that do support status reportingto further improve grant response times in certain instances.

In one example, a method comprises determining, with an optical lineterminal (OLT) coupled to a plurality of optical network terminals(ONTs) that facilitate the transfer of data between a corresponding oneof a plurality of customer network devices and the OLT, an amount ofupstream data associated with a category of service that is waiting at afirst one of the plurality of ONTs to be transmitted upstream to the OLTand computing a number of grant cycles pending (GCPs) with the OLT basedon the determined amount of data associated with the category of servicethat is waiting at the first one of plurality of ONTs to be transmittedupstream to the OLT. The method also comprises computing a number ofGCPs for each of the plurality of ONTs based on a determined amount ofdata associated with the category of service that is waiting to betransmitted upstream to the OLT for each of the plurality of ONTs and,after computing the number of GCPs for each of the plurality of ONTs,granting time slots to the one or more of the plurality of ONTs based onthe number of GCPs computed for each of the plurality of ONTs, whereinthe time slots comprise time slots for upstream communication form theONTs to the OLT.

In another example, an optical line terminal (OLT) couples to aplurality of optical network terminals (ONTs) that facilitate thetransfer of data between a corresponding one of a plurality of customernetwork devices and the OLT. The OLT comprises a control unit thatdetermines an amount of upstream data associated with a category ofservice that is waiting at a first one of the plurality of ONTs to betransmitted upstream to the OLT, computing a number of GCPs for each ofthe plurality of ONTs based on a determined amount of data associatedwith the category of service that is waiting to be transmitted upstreamto the OLT for each of the plurality of ONTs and, after computing thenumber of GCPs for each of the plurality of ONTs, grants time slots tothe one or more of the plurality of ONTs based on the number of GCPscomputed for each of the plurality of ONTs, wherein the time slotscomprise time slots for upstream communication form the ONTs to the OLT.

In another example, a network system comprises a plurality of customernetwork devices and a passive optical network (PON). The PON comprisesan optical line terminal (OLT) and a plurality of optical networkterminals (ONTs) that facilitate the transfer of data between acorresponding one of the plurality of customer network devices and theOLT. The OLT comprises a control unit that determines an amount ofupstream data associated with a category of service that is waiting at afirst one of the plurality of ONTs to be transmitted upstream to theOLT, computes a number of grant cycles pending (GCPs) with the OLT basedon the determined amount of data associated with the category of servicethat is waiting at the first one of plurality of ONTs to be transmittedupstream to the OLT, computing a number of GCPs for each of theplurality of ONTs based on the determined amount of data associated withthe category of service that is waiting to be transmitted upstream tothe OLT for each of the plurality of ONTs and, after computing thenumber of GCPs for each of the plurality of ONTs, grants time slots tothe one or more of the plurality of ONTs based on the number of GCPscomputed for each of the plurality of ONTs, wherein the time slotscomprise time slots for upstream communication form the ONTs to the OLT.

In another example, a non-transitory computer-readable medium comprisinginstructions that, when executed, cause one or more processors todetermine, with an optical line terminal (OLT) coupled to a plurality ofoptical network terminals (ONTs) that facilitate the transfer of databetween a corresponding one of a plurality of customer network devicesand the OLT, an amount of upstream data associated with the category ofservice that is waiting at a first one of the plurality of ONTs to betransmitted upstream to the OLT, compute a number of grant cyclespending (GCPs) with the OLT based on the determined amount of dataassociated with the category of service that is waiting at the first oneof plurality of ONTs to be transmitted upstream to the OLT, compute anumber of GCPs for each of the plurality of ONTs based on the determinedamount of data associated with the category of service that is waitingto be transmitted upstream to the OLT for each of the plurality of ONTsand, after computing the number of GCPs for each of the plurality ofONTs, grant time slots to the one or more of the plurality of ONTs basedon the number of GCPs computed for each of the plurality of ONTs,wherein the time slots comprise time slots for upstream communicationform the ONTs to the OLT.

In another example, a method comprises determining, with an optical lineterminal (OLT) coupled to a plurality of optical network terminals(ONTs) that facilitate the transfer of data between a corresponding oneof a plurality of customer network devices and the OLT, an amount ofupstream data that is waiting at one of the plurality of ONTs to betransmitted upstream to the OLT and determining, with the OLT, an amountof downstream data that is transmitted by the OLT to the one of theplurality of ONTs. The method also comprises increasing the determinedamount of upstream data based on the determined amount of downstreamdata that is transmitted by the OLT to the one of the plurality of ONTs,after increasing the determined amount of upstream data, generating anupstream grant map that grants time slots to the one or more of theplurality of ONTs based on the amount of upstream data determined foreach of the plurality of ONTs and transmitting, with the OLT, theupstream grant map downstream to the plurality of ONTs.

In another example, an optical line terminal (OLT) couples to aplurality of optical network terminals (ONTs) that facilitate thetransfer of data between a corresponding one of a plurality of customernetwork devices and the OLT. The OLT comprises a control unit thatdetermines an amount of upstream data that is waiting at one of theplurality of ONTs to be transmitted upstream to the OLT, determines anamount of downstream data that is transmitted by the OLT to the one ofthe plurality of ONTs, increases the determined amount of upstream databased on the determined amount of downstream data transmitted by the OLTto the one of the plurality of ONTs and after increasing the determinedamount of upstream data, generating an upstream grant map that grantstime slots to the one or more of the plurality of ONTs based on theamount of upstream data determined for each of the plurality of ONTs.The OLT also comprises at least one interface that transmits theupstream grant map downstream to the plurality of ONTs.

In another example, a network system comprises a plurality of customernetwork devices and a passive optical network (PON). The PON comprisesan optical line terminal (OLT) and a plurality of optical networkterminals (ONTs) that facilitate the transfer of data between acorresponding one of the plurality of customer network devices and theOLT. The OLT comprises a control unit that determines an amount ofupstream data that is waiting at one of the plurality of ONTs to betransmitted upstream to the OLT, determines an amount of downstream datathat is transmitted by the OLT to the one of the plurality of ONTs,increases the determined amount of upstream data based on the determinedamount of downstream data transmitted by the OLT to the one of theplurality of ONTs and after increasing the determined amount of upstreamdata, generating an upstream grant map that grants time slots to the oneor more of the plurality of ONTs based on the amount of upstream datadetermined for each of the plurality of ONTs. The OLT also comprises atleast one interface that transmits the upstream grant map downstream tothe plurality of ONTs.

In another example, a non-transitory computer-readable medium comprisinginstructions that, when executed, cause one or more processors todetermine, with an optical line terminal (OLT) coupled to a plurality ofoptical network terminals (ONTs) that facilitate the transfer of databetween a corresponding one of a plurality of customer network devicesand the OLT, an amount of upstream data that is waiting at one of theplurality of ONTs to be transmitted upstream to the OLT, determine, withthe OLT, an amount of downstream data that is transmitted by the OLT tothe one of the plurality of ONTs, increase the determined amount ofupstream data based on the determined amount of downstream datatransmitted by the OLT to the one of the plurality of ONTs, afterincreasing the determined amount of upstream data, generate an upstreamgrant map that grants time slots to the one or more of the plurality ofONTs based on the amount of upstream data determined for each of theplurality of ONTs and transmit, with the OLT, the upstream grant mapdownstream to the plurality of ONTs.

The details of one or more examples of the techniques are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a network system including anexample of an optical line terminal (OLT) that implements grantscheduling techniques described in this disclosure.

FIG. 2 is a block diagram illustrating the OLT of FIG. 1 in more detail.

FIG. 3 is a flowchart illustrating exemplary operation of an OLT inimplementing universal grant scheduling aspects of the techniquesdescribed in this disclosure.

FIG. 4 is a flowchart illustrating exemplary operation of an OLT inimplementing downstream traffic monitoring aspects of the techniquesdescribed in this disclosure.

DETAILED DESCRIPTION

In general, this disclosure describes techniques that provide a grantscheduler for an OLT that may pre-compute certain aspects required todetermine the upstream grant map so as to reduce the requirements forprocessing power and storage capacity in comparison to conventionalimplementations. In accordance with these techniques, the OLT mayconvert upstream data amounts either reported bystatus-reporting-enabled ONTs or monitored by the OLT into grant cyclespending (GCPs) without waiting to receive all of the other statusreports and/or determine the monitored data amounts for those ONTs thatdo not support status reporting. By pre-computing the GCPs as theseupstream data amounts are received and/or determined, the OLT may reducethe number of computations that need be performed during the grant mapgeneration period of time between receiving the last status report ormonitoring the last ONT and sending the upstream grant map downstream tothe ONTs (which is commonly a time period of approximately 125 μs, asnoted above).

During this 125 μs time period, which may be referred to generally as a“grant map generation time period,” the OLT may then only need generatethe grant map from the pre-computed GCPs rather than both transform thedata values to the equivalent of grant cycles and then generate thegrant map from these grant cycles, as is common in conventional systems.While described as a two-step sequential process, during the grant mapgeneration time period, the OLT may continue to convert data amountsinto GCPs, updating existing GCPs with the computed amount of GCPs. Ineffect, the techniques may enable computation of GCPs in a manner thatis independent from the grant map generation time period. Bypre-computing these GCPs, the techniques may reduce the number ofoperations that need to be performed by the OLT during the grant mapgeneration time period as the OLT may not need to both compute the grantcycles and then generate the grant map but only generate the grant mapfrom the GCPs. By reducing the amount of processing power consumed bythe OLTs in this manner, the techniques may enable this grant schedulerto be implemented using less processor intensive hardware, such as afield programmable gate array (FGPA), which may be more cost effectivein terms of the actual cost and subsequent maintenance andtroubleshooting of the OLT.

Moreover, techniques are described to better monitor those ONTs that donot support status reporting so as to improve OLT scheduling ofmonitored ONTs. These monitoring techniques may involve monitoringtraffic sent downstream to these monitored ONTs. Typically, flows oftraffic are monitored rather than ONTs, however, for purposes ofdiscussion, monitoring of ONTs may include monitoring of flows directedto the ONTs as each flow identifies its destination ONT. In response todetecting a marked increase in bandwidth usage by one of these monitoredONTs, the OLT then, in accordance with the techniques, allocates one ormore additional grant cycles pending to that monitored ONT proactively,thereby improving grant response times in certain instances. Theallocation of the number of additional grant cycles pending may be basedon the extent of the increase in downstream bandwidth usage. While thesetechniques may be most beneficial for allocating upstream bandwidth tothose ONTs that do not support status reporting, the techniques may alsobe applied with respect to those ONTs that do support status reportingto further improve grant response times in certain instances.

FIG. 1 is a block diagram illustrating a network system 10 including anexample of an optical line terminal (OLT) 12 that implements the grantscheduling techniques described in this disclosure. While described inthis disclosure with respect to an optical line terminal 12 (“OLT 12”),the techniques may be implemented by any type of network device thatschedules upstream grants over a shared medium, such as a PON, a cablemodem termination system (CMTS), or other networks.

As shown in the example of FIG. 1, network system 10 includes OLT 12, anoptical splitter 14, optical network terminals (ONTs) 16A-16N (“ONTs16”) and customer premises equipment (CPE) 18A-18Z (“CPE 18”). OLT 12generally represents an optical network device that resides in a centraloffice of a service provider and serves as a point of origination forfiber-to-the-premises (FTTP) transmissions. OLT 12 generally performsoperations to maintain connectivity and schedule data transmissionsbetween OLT 12 and ONTs 16. OLT 12 may, for example, performauto-discovery to discover new ONTs 16, range ONTs 16 to adjust datatransmissions to reduce conflicts, schedule upstream data transmissionfrom ONTs 16 to OLT 12, and otherwise manage fiber line 20 coupling OLT12 to each of ONTs 16.

Optical splitter 14 represents a device that splits an optical signalinto two or more copies of the optical signal. In other instances,optical splitter 14 represents a device that splits an optical signalcomposed of a number of different wavelengths into at least twodifferent optical signals that each has a different subset of thewavelengths. Optical splitter 14 is presumed to be a passive opticalsplitter that merely splits an optical signal into two or more copies orreplicas of the optical signal. In effect, optical splitter 14 splitsoptical signals sent over optical line 20 into a number of differentsub-signals so that these sub-signals can be sent via optical fiberlines 21A-21N (“optical fiber lines 21” or “optical lines 21”).

OLT 12 generally includes one physical interface to service a number ofONTs, such as ONTs 16, where OLT 12 multiplexes a number of differentoptical signals of different wavelengths into a single optical signalthat can be sent via the single physical interface to optical fiber line20. Optical splitter 14, in this context, serves to copy the multiplexedoptical signal and relay a copy of each of the optical signals to eachone of ONTs 16, where this copying is commonly referred to as“splitting.” This splitting, however, does not involve any activeswitching, but instead merely refers to creating a copy of any givenoptical signal and sending a copy of this signal to each of ONTs 16.Optical splitter 14, while referred to as a splitter, may also include acombiner that combines the various optical signal sent upstream fromONTs 16 to OLTs 12 into a single optical signal. Optical splitter 14 iscommonly not powered and, as a result, may be referred to as “passive”both because it is not powered and because it does not actively route orswitch optical signals.

Each of ONTs 16 represents an optical network device that terminates acorresponding one of optical fiber lines 21. ONTs 16 receive theircorresponding optical signals and further demultiplex these signals intodifferent component parts, such as a voice component, a video componentand a data component. ONTs 16 then forward these different componentsvia various subscriber networks (which, in this case, may include avoice, video and data network or some combination thereof) to CPE 18.CPE 18 each represents any device capable of receiving and processingthe different components of the optical signal, such as a set-top box(STB), a digital recorder, a personal media player (PMP), a cellularphone (including so-called “smart phones”), a voice over Internetprotocol (VoIP) telephone, an ordinary plain-old telephone system (POTS)phone, a television, a wireless network enabled television, a desktopcomputer, a laptop computer, a so-called “netbook,” a personal digitalassistant (PDA), a server, a workstation, a wireless access point (WAP),a hub, and a switch. CPE 18 receives these different components of theoptical signal and presents these varying components for consumption bycustomers that own and operate CPE 18.

As noted above, each of CPE 18 typically receives a copy of everyoptical signal sent downstream from OLT 12 to any one of CPE 18, as link20 is shared by CPE 18 and optical splitter 14 does not actively switchor router these optical signals. Given the large amount of bandwidthprovided by optical networks systems, such as network system 20 shown inthe example of FIG. 1, this form of passive networking that involvesreplication or copying was widely adopted for its ease of maintenanceand low cost. This passive form of data distribution is typicallyconsidered “easy to maintain” in that optical splitter 14 is not poweredand does not require any extensive configuration. Typically, opticalsplitter 14 is installed in a post or other outside plant enclosure nearthe customer premises by inserting this splitter 14 in the enclosure andcoupling splitter 14 to the proper links Once properly inserted andcoupled, little if any other configuration is required for opticalsplitter 14 to begin properly “splitting” or copying the optical signalson a passive basis.

The passive form of network is lower in cost than actively switchingnetworks because it does not require power, which can be costly whenhaving to power hundreds if not thousands of active switches. Moreover,un-powered devices, such as passive splitter 14, may be, as noted above,easier to maintain, leading to lower maintenance associated costs overcomparable active optical networks. For this reason, passive opticalnetworks were widely deployed by service provider networks to provideso-called “triple-play” package (involving delivery of a combinedpackage of video, data and voice services) to subscribers.

In contrast to downstream communications from OLT 12 to ONTs 16 whereall such downstream communications are combined over shared link 22 andthen replicated to each of ONTs 16, upstream communications from ONTs 16to OLT 12 are managed by OLT 12 through implementation of a downstreambandwidth allocation (DBA) algorithm. Initially, service providernetworks deployed basic OLT and ONTs that implemented basic DBAalgorithms. For example, OLT 12 assigned time slots to ONTs 16 duringwhich the ONTs 16 may communicate upstream based solely on the serviceagreement between the customer associated with each of ONTs 16 and theservice provider. Typically, OLT 12 implemented a static tableidentifying a subscribed-to amount of bandwidth for each of the servicesto which each ONT 16 subscribed regardless of whether the customeractually utilized this assigned upstream bandwidth. These time slots maybe variable-sized time slots or fixed-sized time slots, althoughcommonly, OLT 12 allocates variable-sized time slots in the mannerdefined by the GPON or other PON standards.

As data services grew in adoption (with the notable almost exponentialsurge in Internet data traffic on a yearly basis) and more data that wascommonly provided via different communication media converging with theoffering of triple-play packages, the generous amount of upstreambandwidth offered by passive optical networks was consumed by burstyrequests for Internet traffic during certain periods of the day, e.g.,such as when consumers arrived home from work or when they got up in themorning. Not wanting to increase the outlay of additional fiber linksand deployment of additional OLTs and ONTs to satisfy this relativelybursty and often periodic upstream bandwidth consumption, serviceproviders sought ways to oversubscribe the network while stillsatisfying minimum bandwidth requirements for services specified insubscription contracts (which are also often referred to as “serviceagreements”) with consumers. Responding to this request, optical networkdevice manufactures soon provided updated OLTs and ONTs that implementedmore advanced DBA algorithms. While this is commonly considered thereasons optical network device manufactures provided these updated OLTsand ONT, there are any number of other reasons and context fordeveloping updated OLTs and ONTs. The above is provided merely forcontext and should not be considered to limit the techniques describedin this disclosure in any way.

For example, some PON standards, such as the GPON standard set forth ina standard identified as an International Telecommunication Union (ITU)Telecommunication Standardization Sector (ITU-T) G984.2 standard, beganintroducing a more advanced DBA algorithm that specified a way ofpolling or querying ONTs for an approximate amount of data waiting to besent upstream to the OLT. In response to this query, the ONTs issuedstatus reports indicating the approximate amount of data waiting to besent upstream to the OLTs for a given traffic container (or “T-CONT”).The term “traffic container” generally refers to any container forstoring upstream data (such as a buffer, memory, virtual memory, virtualbuffer, cache or the like). Typically, T-CONTs are provided for each ofthe data, voice and television services as well as for other specialtraffic and may represent a way to differentiate different types oftraffic that have different service classes. In any event, this statusreporting form of DBA enables OLTs to actively determine an amount ofdata waiting to be sent upstream for each of its ONTs and thenproactively assign or grant time slots to each of the ONTs so as toaccommodate oversubscription of shared links, such as link 22.

To illustrate, assuming OLT 12 implements this more advanced form ofstatus reporting (SR) DBA, OTL 12 may poll ONTs 16 and receive statusreports from each of ONTs 16 regarding an approximation of a currentamount of data waiting to be sent upstream to OLT 12. In this example,it is also assumed that half of ONTs 16 have data waiting to be sentupstream to OLT 12 while the other half of ONTs 16 do not have datawaiting to be sent upstream to OLT 12. Collectively, ONTs 16 may beentitled to more upstream bandwidth than that physically capable ofbeing provided by shared link 22, which results in oversubscription ofshared link 22. Yet, considering that this upstream traffic is bursty innature, shared link 22 may accommodate approximately two thirds of ONTs16 at any one time when providing ONTs 16 with their maximum upstreambandwidth to which they are entitled under the service agreement.Without SR DBA, OLT 12 may inefficiently allocate bandwidth to the halfof ONTs 16 that do not have data waiting to be sent upstream to OLT 12.By polling these ONTs 16, however, OLT 12 may more accurately grantupstream time slots to only the half of ONTs 16 that actually have datawaiting to be sent upstream to OLT 12. In this manner, SR DBAaccommodates oversubscription of shared link 22.

While SR DBA provides many benefits in terms of granting upstreambandwidth, often legacy ONTs are deployed by service providers alongsidethese more advanced forms of ONTs. To provide a similar form of DBA withrespect to these legacy ONTs, OLTs were deployed or upgraded to supporta form of DBA referred to as traffic monitoring DBA. In trafficmonitoring DBA, the OLT initially grants these upstream time slots(which refer to time slots during which these legacy ONTs may transmitdata upstream to the OLT) in accordance with their service agreements.The OLT then monitors the transmission of data during each of thesegranted upstream time slots to determine whether each ONT has any datato transmit upstream, and, if they have data to send upstream, how muchdata was sent. The OLT then maintains a table or other data structure tostore this historical upstream data transmission information. Goingforward, the OLT refers to this table when granting upstream time slotsto the ONTs. ONTs may additionally request upstream time slots in thisimplementation so as to provoke a monitoring session and thereby gainaccess to additional time slots. Alternatively, the OLT may periodicallygrant each of the ONTs an upstream time slot to enable this monitoringand data collection.

Such a traffic monitoring DBA may suffer, however, in certain instancesor contexts due to the reactive nature of traffic monitoring DBA. Thatis, this traffic monitoring DBA may be considered “reactive” in that theOLT only learns of upstream data waiting to be sent by the ONT aftersome data has been sent by that ONT and then reacts to this data toassign the ONT more upstream time slots if the ONT fully utilizes thepreviously assigned time slots. Such reactive scheduling of upstreambandwidth may result in scheduling increasingly more upstream time slotsfor an ONT that has a lot of upstream data waiting to be sent to theOLT, which may result in inefficiencies in certain contexts.

For example, when a protocol by which this data is to be sent includessome bandwidth limiting or windowing mechanism that determines a numberof packets that may be sent prior to receiving an acknowledgement basedon a time to respond to downstream data packets sent by the other deviceterminating the session (such as a transmission control protocol orTCP), the reactive nature of traffic monitoring DBA may result in agrant time that delays transmission of upstream data to the extent thatthese protocols impose a what limit on the number of packets that may besent via the windowing mechanism. The OLT then monitors this ONT, notingthat the ONT is only transmitting during a portion of granted time slots(due to the TCP packet limit), whereupon the OLT then allocates lesstime slots despite the fact that this ONT may still have large amountsof data waiting to be sent. As the OLT continues to send this data, TCPmay enlarge the number of packets that may be sent (which may bereferred to as a “window”), whereupon the OLT may then assign more timeslots. This process may continue with TCP expanding while the OLTcontracts bandwidth allocations, resulting in bandwidth utilizationinefficiencies.

In any event, OLTs typically schedule those ONTs that implement SR DBAseparately from those ONTs that do not support SR DBA, as thesedifferent grant scheduling algorithms are typically implementeddifferently and rely on different scheduling periods. Moreover, whenperforming traffic monitoring, the OLT may behave reactively, as notedabove. When performing SR DBA, however, the OLT may be considered to actproactively in that the OLT learns of this data before it is sent andmay adjust the number of time slots granted accordingly. This fragmentedtreatment to scheduling grants of upstream time slots often results inoverly complicated scheduling algorithms. Often, when attempting toschedule these ONTs collectively, the OLT may provide disjointedtreatment of ONTs depending on whether they support SR DBA or not,resulting in varying degrees of service for different customers despitethe fact that these different customers may subscribe to the same typeand level of service.

In addition, when implemented within the same scheduler, the grantscheduler of the OLT usually waits until a scheduling round (duringwhich the OLT may receive data identifying an amount of data to betransmitted upstream from each ONT to which the OLT connects and/ormonitor upstream data communications from the ONT) has completed priorto computing the grant map that allocates the upstream time slots to theOLTs during the upcoming upstream transmission period. The grantscheduler waits until the completion of the scheduling round duringwhich it receives or monitors this upstream information as without thisinformation the grant scheduler is unable to adequately assess which ofthe OLTs require upstream time slots. In the time between the completionof the scheduling round and generating this grant map (which may beapproximately 125 microseconds (μs)), the OLT is required to determineand generate this grant map. Yet, computing this grant map involves anumber of different mathematical computations, some of which involvemultiplications and/or divisions, which may take many processor cyclesto complete.

Moreover, given the dynamic nature of both SR and traffic monitoring DBAin conjunction with the various weights that may be assigned toaccommodate different service classes or levels and the necessity ofgenerally meeting the minimum requirements specified in the servicecontract, the grant scheduler may have to perform a significant numberof computations in what may be considered a very short period of time.Typically, implementation of a grant scheduler of this nature involvessignificant processing resources and/or specifically designed dedicatedhardware, such as application specific integrated circuits (ASICs).While such components are not uncommon, these components increase thecost in terms of both initial purchase price and potential maintenancerequirements.

Furthermore, various PON standards are frequently being revised orotherwise altered. Given that ASICs are specially designed to implementthese standards, changes to these ASICs so as to implement the updatedor revised standards are often difficult and may, in some instances,require that completely new ASICs be designed. Given the inflexibilityof ASICs to accommodate some PON revisions, ASIC-based OLTs may beexpensive to maintain over the life of multiple PON revisions,especially when such revisions require a new ASIC be developed andinstalled across what may be tens, if not hundreds, of OLTs. ASICs may,therefore, generally be considered inflexible with respect to anychanges and result in increased administrative and other maintenancecosts. In accordance with the grant scheduling techniques described inthis disclosure, OLT 12 includes a universal grant scheduler unit 24that potentially reduces the number of computations required to beperformed during this short period of time between collecting all of thestatus reports and transmitting the grant map. By reducing the number ofcomputations, universal grant schedule unit 24 may not require thesignificant hardware resources or specially designed dedicated hardwareconventionally required to perform these operations during what isconventionally thought of as the grant map generation period of timebetween determining the last amount of data to be sent upstream by ONTs16 and transmitting the grant map, which may reduce costs associatedwith manufacturing OLT 12.

In some instances, the techniques may reduce the processing requirementsduring this short period of time post data collection and pre-grant maptransmittal such that universal grant scheduler unit 24 may beimplemented as programmable hardware, such as a field programmable gatearray (FPGA). There are a number of benefits associated with FPGAsincluding flexibility and rapid prototyping (in comparison toprototyping and development of ASICs), cost in terms of nonrecurringengineering expense (especially in comparison to designing an ASIC),reliability that is on par with dedicated hardware (including ASICs),and long-term maintenance benefits in that FPGAs are field upgradeableto account for changing design requirements.

To reduce the number of computation, universal grant scheduler unit 24is configured to operate on what is referred to in this disclosure as“grant cycles pending” or “GCPs.” GCPs represent an intermediate form ofthe amount of data waiting to be sent upstream by ONTs 16 in that GCPsrepresent the number of grant cycles that would be consumed to transmitall of the data waiting to be sent upstream at each of ONTs 16. Byconverting the data amounts into GCPs for each of ONTs 16, universalgrant scheduler unit 24 need not perform this conversion during thegrant map generation period of time, thereby significantly reducing thenumber of operations that need be performed during this shortened grantmap generation period of time. This form of abstraction from amounts ofdata to GCPs hides the underlying DBA algorithm employed to learn ofthese amounts of data from universal grant scheduler unit 24. Instead,universal grant scheduler unit 24 may be considered “universal” in thesense that it can schedule upstream time slot grants without regard towhether ONTs 16 support SR DBA or not. By implementing the techniquesdescribed in this disclosure, universal grant scheduler unit 24 may thenbase the allocation of upstream bandwidth allocation on grant cyclespending, fully unaware of whether these grant cycles pending correspondto traffic monitored, reported data amounts or any other way by whichdata amounts are reported. By effectively removing the responsibility ofcollecting this data and converting this data into grant cycles,universal grant scheduler unit 24 may more efficiently generate thegrant map.

To illustrate, OLT 12 may first determine an amount of upstream datathat is waiting at a first one of ONTs 16 (e.g., ONT 16A) to betransmitted upstream to OLT 12. Typically, OLT 12 determines this amountof data with respect to a category of services, which may include aquality or class of service or any other identifier that identifies acategory of service to which this data or traffic may be associated.ONTs 16 may generally store data associated with different categories ofservice to different queues (or traffic containers as they are commonlyabstracted in the optical network context), whereupon OLT 12 maydetermine the amount of data that is associated with this category ofservice. In some instances, OLT 12 may determine an amount of dataregardless of the category of service.

OLT 12 may determine this amount via traffic monitoring DBA or viastatus reports sent by ONT 16A to OLT 12 in the manner described above.When performing traffic monitoring DBA, OLT 12 may determine a categoryof service of monitored traffic by determining a protocol or otheraspect of the packets that is associated with different types orcategories of service. For example, hypertext transfer protocol (HTTP)traffic is generally identified by an HTTP header and use of InternetProtocol (IP) port 80. OLT 12 may maintain or otherwise store dataidentifying associations between certain protocol/port pairs and acategory of service.

Regardless, OLT 12 may then, prior to determining an amount of data thatis waiting at a second one of ONTs 16 (e.g., ONT 16N) to be transmittedupstream to OLT 12, compute a number of grant cycles pending (GCPs)based on the determined amount of data that is waiting at ONTs 16A to betransmitted upstream to the OLT 12. While not shown in the example ofFIG. 1 for ease of illustration purposes, OLT 12 may include atranslator unit that converts data amounts into GCPs using a conversionformula. The conversion formula may be statically defined or dynamicallyspecified or configurable by a user. This translator of OLT 12 thenstores the computed number of GCPs for the ONT 16A to a GCP table, whichagain is not shown in FIG. 1 for ease of illustration purposes.

In this manner, a portion of the process that is conventionallyperformed during the short period of time after determining the lastamount of data waiting to be sent upstream by ONTs 16 and transmittingthe grant map may be performed at least in part prior to this shortenedgrant map generation period of time. As a result, universal grantscheduler unit 24 may not be required to also convert these amounts ofdata to grant cycles during this shortened period of time, therebypotentially reducing the number of operations that need be performedduring this period of time. Instead, universal grant scheduler unit 24,after the translator stores the computed number of GCPs to the GCP tablefor each of the plurality of ONTs 16, determines an upstream grant mapthat grants time slots (which may also be referred to as “grant cycles”)to one or more of ONTs 16 based on the computed number of GCPs stored tothe GCP table for each of ONTs 16. Universal grant scheduler unit 24 maystill implement the weighted round robin algorithm or any otherscheduling algorithm only with respect to GCPs instead of amounts ofupstream data waiting at ONTs 16 to be sent upstream. Universal grantscheduler 24 then transmits via an interface coupling OLT 12 to link 22and thereby ONTs 16 the upstream grant map downstream to ONTs 16.

In addition, OLT 12 includes a downstream monitoring unit 26 that mayenhance how grant cycles pending are allocated to traffic monitored onesof ONTs 16 in accordance with various aspects of the techniquesdescribed in this disclosure. Downstream monitoring unit 26 mayrepresent a unit that monitors downstream traffic (i.e., trafficreceived by OLT 12 that is destined to one or more of ONTs 16) typicallyfor those of ONTs 16 that do not support SR DBA. However, whiledescribed as being typically applied to those ONTs 16 that do notsupport SR DBA, the techniques may implemented such that downstreammonitoring unit 26 monitors traffic for one or more and potentially allof ONTs 16 regardless of whether these ONTs 16 support SR DBA or not.

Downstream monitoring unit 26 may determine which of ONTs 16 to monitorbased on some configuration data input by an administrator.Alternatively, downstream monitoring unit 26 may be configured toautomatically monitor downstream traffic for those of ONTs 16 that donot respond to a status request that requests an approximate amount ofupstream data is waiting to be sent upstream at each of ONTs 16 to OLT12. The term “automatically” is used in this context to mean that theadministrator does not indicate for which of ONTs 16 that downstreammonitoring unit 26 is to monitor their downstream traffic. Rather,downstream monitoring unit 26 may automatically determine without beingspecifically configured by the administrator which of ONTs 16 do notsupport SR DBA based on status reports received from ONTs 16. Downstreammonitoring unit 26 may then generate a list or any other type of datastructure defining those of ONTs 16 that did not respond with a statusreport and monitor those of ONTs 16 specified within the list or otherdata structure.

Downstream monitoring unit 26 may identify downstream traffic intendedfor one or more of ONTs 16 based on, for example, a layer two (L2)address associated with ONTs 16 or any other identifier associated withONTs 16, such as a PON ID, a virtual local area network (VLAN) tag, or alayer three (L3) address. Downstream monitoring unit 26 may maintain atable or other data structure having entries for each of the ONTs 16 forwhich downstream traffic monitoring has been enabled. To each entry,downstream monitoring unit 26 may store data defining an amount ofdownstream traffic sent to each of ONTs 16. Periodically or, in someinstances, in response to updating an entry, downstream monitoring unit26 may forward this updated data to the translator unit, whichdetermines a number of additional GCPs for each of these ONTs 16 basedon the amount of downstream traffic sent to each of the correspondingones of ONTs 16. Again, this translator unit may employ a conversionformula or any other mechanism for determining how to convert the amountof downstream traffic into additional GCPs to assign to each of theseONTs 16 for delivery of upstream data to OLT 12. This translator unitmay update entries in the GCP table that correspond to each of thedownstream monitored ones of ONTs 16 with the additional GCPs so as toallocate additional upstream bandwidth to these ones of ONTs 16.

By attempting to proactively schedule more upstream bandwidth for thoseof ONTs 16 that do not support SR DBA, the techniques may reduce whatmay be characterized as the “thrashing” of bandwidth allocation incertain contexts, such as in the TCP windowing context described above.To illustrate, consider the TCP windowing example above, where the OLTfails to grant a time slot in time for the OLT to response to a TCPpacket sent by another device that terminates the TCP session. In thisexample, downstream monitoring unit 12 of OLT 12 may proactively addadditional GCPs for those of ONTs 16 receiving downstream data and thatdo not support SR DBA. Universal grant scheduler unit 24 in this contextmay then, when generating the grant map, determine that these ones ofONTs 16 have relatively more upstream data waiting to be sent than otherones of ONTs 16, granting these ones of ONTs 16 additional upstream timeslots. These ones of ONTs 16 may then respond more quickly to thedownstream data, ensuring that the TCP windowing mechanism does notdrastically reduce the window (i.e., the number of packets that theseones of ONTs 16 may send in response to an acknowledgement by the otherdevice terminating the TCP session). In this sense, the enhanced trafficmonitoring DBA aspects of the techniques set forth in this disclosuremay attempt to add a certain amount of proactivity to what isconventionally considered a reactive form of DBA to potentially reduceor possibly eliminate the thrashing of bandwidth allocation in certaincontexts.

Although the grant scheduling and downstream monitoring aspects of thetechniques are described as being implemented in conjunction with oneanother, the grant scheduling and downstream monitoring aspects of thetechniques may not necessarily be implemented in this manner. In someinstances, OLT 12 may implement only the grant scheduling techniques oronly the downstream monitoring aspects of the techniques described inthis disclosure without implementing the downstream monitoring or grantscheduling aspects of the techniques described in this disclosure.Consequently, while described as being implemented by the same OLT,i.e., OLT 12 in this example, the techniques should not be limited inthis respect.

While described in this disclosure generally with respect to passiveoptical networks (PONs), the techniques described in this disclosure maybe implemented with respect to any type of passive optical network, suchas a broadband PON (BPON), a gigabyte PON (GPON), an Ethernet PON(EPON), and the like. For example, optical transport system 10 mayfunction in accordance with the giga-bit PON (GPON), baseband PON(BPON), or Ethernet PON (EPON) standards, or other standards. The GPON,BPON, and EPON standards are defined by ITU-T G984.2 and G983.3, ITU-T983.1, respectively.

Moreover, while the techniques are described in reference to opticalnetwork terminals, the techniques may be implemented by any networkdevice capable of terminating an optical link or line and providing datatransmitted via the optical link or line to a customer or subscribernetwork, including an optical network unit (ONU). In some instances, theterm ONU is used interchangeably with the term ONU, and the techniquesshould not be limited to either an ONT or ONU but to any network devicecapable of terminating an optical link or line and providing datatransmitted via the optical link or line to a customer or subscribernetwork.

FIG. 2 is a block diagram illustrating OLT 12 of FIG. 1 in more detail.In the example of FIG. 2, OLT 12 includes a control unit 30 andinterfaces 32A-32N (“interfaces 32”). Control unit 30 may represent oneor more processors (not shown in example of FIG. 2) that executesoftware instructions, such as those used to define a software orcomputer program, stored to a computer-readable storage medium (again,not shown in the example of FIG. 2), such as a storage device (e.g., adisk drive, or an optical drive), or memory (such as Flash memory,random access memory or RAM) or any other type of volatile ornon-volatile memory, that stores instructions to cause a programmableprocessor to perform the techniques described herein. Alternatively,control unit 30 may represent dedicated hardware, such as one or moreintegrated circuits, one or more Application Specific IntegratedCircuits (ASICs), one or more Application Specific Special Processors(ASSPs), one or more Field Programmable Gate Arrays (FPGAs), or anycombination of one or more of the foregoing examples of dedicatedhardware, for performing the techniques described herein.

Each of interfaces 32 represents an interface for interfacing with aphysical communication medium, such as an optical fiber link 20 andoptical fiber link 22. In the example of FIG. 2, interface 32A isassumed to couple to optical fiber link 22 while interface 32N isassumed to couple to optical fiber link 20. An interface card (IFC) maycomprise one or more of interfaces 32, which in this context may bereferred to as ports. Each IFC may be inserted into a slot of a chassisthat couples to control unit 30 via a backplane or other high-speedinterconnection.

Control unit 30 includes universal grant scheduler unit 24 anddownstream monitoring unit 26, where were described above with respectto the example of FIG. 1. Universal grant scheduler unit 24 represents aunit that implements the grant scheduling aspects of the techniquesdescribed in this disclosure to generate a grant map scheduling timeslots during which upstream data may be sent by one or more of ONTs 16based on grant cycles pending or GCPs rather than actual or approximateddata amounts determined to be waiting at ONTs 16 for upstreamtransmission. Downstream monitoring unit 26 represents a unit thatmonitors downstream traffic 40 received by ONT 12 via interface 32A overlink 22 for delivery to one or more of ONTs 16.

Control unit 30 also includes a status reporting downstream bandwidthallocation (SR DBA) unit 34 (“SR DBA unit 34”), a traffic monitoring(TR) DBA unit 36 (“TM DBA unit 36”) and a translator unit 38. SR DBAunit 34 represents a unit that implements SR DBA as specified by anyapplicable PON standard, such as the GPON standard set forth by theITU-T G984.2. TM DBA unit 36 represents a unit that monitors upstreamtraffic 42 received via interface 32 via link 20 from ONTs 16 for one ormore of ONTs 16 and generates additional GCPs in accordance with variousaspects of the techniques described in this disclosure. Translator unit38 represents a unit that translates actual or approximate data amountsof traffic waiting upstream (and downstream in instances where both theuniversal grant and downstream traffic monitoring aspects of thetechniques are implemented together) into GCPs.

Initially, an administrator or other user may interface with a userinterface presented by a user interface module or unit of control unit30, which is not shown for ease of illustration purposes. Theadministrator may configure or otherwise specify monitoring parameters44 for downstream monitoring unit 26 and monitoring parameters 46 for TMDBA unit 36. Both monitoring parameters 44 and 46 may specify those ofONTs 16 that downstream monitoring unit 26 should monitor or otherwiseconfigure downstream monitoring unit 26 and TM DBA unit 36 toautomatically detect those ONTs 16 that do not support SR DBA based onstatus reports received from ONTs 16, such as status reports 50 (“statrep 50”), in the manner described above. Monitoring parameters 44 mayalso define a threshold or other metric to which downstream monitoringunit 26 compares monitored downstream traffic amounts stored todownstream table 52.

Downstream monitoring unit 26 may also store downstream table 52 suchthat this table 52 includes an entry for each of those ONTs 16 specifiedby monitoring parameters 44 and/or that do not support SR DBA (asautomatically detected based on status reports 50. Each entry stores anamount of data sent downstream to corresponding ones of ONTs 16.Downstream monitoring unit 26 may compare the amount stored to eachentry to this threshold and, if the amount exceeds the threshold,downstream monitoring unit 26 may forward this amount to translator unit38, which effectively adds additional GCPs to an entry in GCP table 54associated with that one of ONTs 16. If the amount does not exceed thethreshold or other configurable or pre-defined metric, downstreammonitoring unit 26 continues to monitor downstream traffic 40 and updatedownstream table 52.

Monitoring parameters 44 may also define a wasting or decay functionthat downstream monitoring unit 26 may apply to clear or otherwisereduce amounts stored to downstream table 52. Downstream monitoring unit26 may reduce amounts stored to downstream table 52 as a function oftime so that downstream monitoring unit 26 may only report surges indownstream traffic to any given one of ONTs 16 that may require theseones of ONTs 16 to quickly respond so as to avoid thrashing bandwidthallocation when the TCP or other protocols windowing or bandwidthlimitation mechanisms interfere with bandwidth allocation by OLT 12.

In any event, once configured, the administrator may enable ONT 12 tobegin receiving and forwarding both downstream traffic 40 and upstreamtraffic 42. Interface 32A may receive downstream traffic and replicatethis traffic, forwarding this replicated downstream traffic 40 todownstream monitoring unit 26. Interface 32A may replicate this traffic40 so that it can forward the original traffic via interface 32N to ONTs16 while downstream monitoring unit 26 performs its monitoring tasks.Likewise, interface 32N may receive upstream traffic 42 from ONTs 16 andreplicate this traffic 42 while sending the original upstream traffic 42upstream via interface 32A. For this reason, replicated downstreamtraffic 40 and replicated upstream traffic 42 is shown as a dashed lineto indicate that it represents replicated traffic rather than theoriginal traffic, which may be switches or otherwise forwarded uponreceipt to reduce latency. Although described with respect to replicatedtraffic 40, 42, the techniques may be implemented with respect to OLTsthat do not replicate traffic but operate on the original traffic. Thetechniques should therefore not be limited in this respect to theexample of FIG. 2.

As noted above, OLT 12 does not schedule transmission of downstreamtraffic 40 downstream to ONTs 16 considering that link 20 is shared byall of ONTs 16 and therefore each of ONTS 16 receive downstream traffic40 whether destined for that particular one of ONTs 16 or not. ONTs 16then filter downstream traffic 40 that is not destined for themtypically by performing hardware-level layer two address filtering, suchas media access control (MAC) address filtering. Consequently, OLT 12forwards downstream traffic 40 upon receipt of this traffic 40 unlessthese time slots during which this downstream traffic is to be forwardedhas been reserved for upstream transmissions from ONTs 16 to OLT 12.

In order to schedule these upstream time slots, SR DBA unit 34 mayinitially issue a status request 48 (“stat req 48”) over link 20 viainterface 32N to ONTs 16. Those of ONTs 16 that support SR DBA mayrespond with one of status reports 50. SR DBA unit 34 may parse thesestatus reports 50 to extract an amount of data waiting at the one ofONTs 16 that sent the corresponding one of status reports 50. The amountof data reported may be exact in or approximated. For example, theamount of data may be reported as a number of data blocks, where a blockmay represent one or more bytes. Thus, if this block is configured to be4 bytes and an ONT has 42 bytes waiting to be sent upstream, the ONT mayreport that it has 11 blocks (which the OLT will interpret as 44 bytes)waiting to be sent upstream, which is only an approximate amount of datawaiting to be sent upstream as the ONT actually has 42 bytes. Typically,if the amount of data waiting to be sent upstream is small (e.g.,smaller than 128 kilobytes (KBs)), those of ONTs 16 that support SR DBAmay specify the amount approximately by way of a signaling a number ofblocks. However, if the amount of data waiting to be sent upstream islarge (e.g., greater than 128 KBs), those of ONTs 16 that support SR DBAmay specify a code indicating whether the amount of data waiting to besent upstream is between 128 KBs and 256 KBs, between 256 KBs and 512KBs, and so on.

SR DBA unit 34 may forward status reported amounts 53 to translator unit38, which employs conversion formula 54 to convert status reportedamounts 53 into GCP 56. SR DBA unit 34 may also provide a list 51 ofthose ONTs 16 that do not support SR DBA to downstream monitoring unit26 and TM DBA unit 36, which may enable these units 26, 36 to determinewhich of ONTs 16 to monitor when configured to automatically monitorthose ONTs 16 that do not support SR DBA. SR DBA unit 34 may determinethis list 51 based on status reports 50. For those ONTs 16 that SR DBAunit 34 did not receive one of status reports 50, SR DBA unit 34 may addthose ONTs 16 to list 51.

Whether configured to automatically monitor those of ONTs 16 that do notsupport SR DBA or configured with a list of ONTs 16 to monitor viamonitoring parameters 44, downstream monitoring unit 26 may monitordownstream traffic 40, updating downstream table 52 to log the amountsof data sent downstream to each of these monitored ones of ONTs 16.Downstream monitoring unit 26 may periodically or, in response toupdating downstream table 52, apply one or more of the above notedthresholds to determine whether to report this downstream data amountfor one or more of the monitored ones of ONTs 16.

As noted above, if a downstream data amount stored to downstream table52 exceeds one of the thresholds, downstream monitoring unit 26 mayforward this downstream data amount 58 to translator unit 38 (ininstances where both the downstream monitoring and universal grantscheduling aspects of the techniques are implemented in conjunction withone another). Translator 38 applies conversion formula 54 to convertthis downstream data amount 58 to GCPs 56, which translator 38 thenstores to GCP table 54. If the amounts stored to downstream table 52 donot exceed the threshold, downstream monitoring unit 26 continues toupdate downstream table 52 based on downstream traffic 40. Downstreammonitoring unit 26 may also apply a wasting or decay function todecrement the amounts stored to downstream table 52 periodically asnoted above.

Universal grant scheduler unit 24 may, meanwhile, generate an initialgrant map 60 allocating each of ONTs 16 (or those of ONTs 16 that areactive or otherwise powered on) at least one upstream time slot duringwhich each of ONTs 16 may communicate data upstream. This initial grantmap 60 may facilitate upstream bandwidth monitoring performed by TM DBAunit 36. If all of ONTs 16 support SR DBA, then universal grantscheduler unit 24 may forgo this initial grant map 60 and insteadgenerate a grant map 60 that allocates time slots based on GCPs 56translated from reported data amounts 53 by translator unit 38.Otherwise, if not all of ONTs 16 support SR DBA, this initial grant map60 that allocates at least one time slot to each of ONTs 16 (assumingthat all of ONTs 16 are active) provides TM DBA unit 36 an opportunityto monitor upstream bandwidth transmissions for each of ONTs 16 or, atleast, those of ONTs 16 specified by list 51.

TM DBA unit 36 receives this initial grant map 60 and uses this initialgrant map 60 to determine when to monitor upstream traffic 42, i.e.,which of the upstream time slots correspond to ONTs 16 that do notsupport SR DBA. Alternatively, TM DBA unit 36 may monitor all upstreamtraffic 42 without reference to grant map 60. TM DBA unit 36 thenmonitors upstream traffic 42, logging amounts of data sent upstream toupstream table 56, which may be similar to downstream table 52 only formonitoring upstream traffic 42. TM DBA unit 36 may then report upstreamdata amounts 62 stored to upstream table 56 after monitoring those ONTs16 that do not support SR DBA. While described as involving a table 56,the techniques may be implemented such that TM DBA unit 36 merelybuffers a data amount for each of ONTs 16 and immediately reports thisdata amount rather than storing a data amount to a table. Whether storedto a table or not, TM DBA unit 36 forwards upstream data amounts 62 totranslator unit 38, which applies conversion formula 54 to these amounts62 to convert amounts 62 into GCPs 56. Translator unit 38 then storesGCPs 54 for those of ONTs 16 that do not support SR DBA to acorresponding entry of GCP table 54.

As described above, translator unit 38 converts data amounts 53, 58 and62 to GCPs 56 prior to the grant map generation period of time betweenreceiving the last one of status reports 50 or monitoring and reportingthe last one of upstream data amounts 62 and the actual generation ofgrant map 64. In converting amounts 53, 58 and 62 to GCPs 56 prior tothe grant map generation time period, translation unit 38 mayeffectively reduce the number of operations universal grant schedulerunit 24 need perform during this short grant map generation time period.Translation unit 38 stores these GCPs 56 to GCP table 54.

Universal grant scheduler unit 25 then, during the grant map generationtime period, evaluates GCP table 54 in view of parameter table 66 andservice level agreement (SLA) table 68 (“SLA table 68”). Parameter table66 may define a maximum bandwidth supported by link 20 as well as otherparameters relevant to the delivery of data via the PON, including atotal PON bandwidth available to the DBA scheduler, a grant timeoverhead (which includes a guard band, preamble and delimiter) and agrant size to use for each OLT (actually, for each traffic container orso-called “T-CONT” provided by each OLT). SLA table 68 may defineservice level agreements or what may be referred to as “service classes”for various services to which customers may describe. Such serviceclasses may define a maximum permitted bandwidth, minimum guaranteedbandwidth, minimum and maximum latency requirements and other servicelevel metrics that may limit or otherwise define a level of serviceprovided to customers that subscribed to that level of services. SLAtable 68 may further specify an association between each of ONTs 16 andone or more SLA agreements, where more than one SLA agreement may beassociated to one of ONTs 16 when that ONT delivers more than oneservice, such as voice, data and video services. Universal grantscheduler unit 24 may implement a round-robin scheduling algorithm, aweighted-round-robin scheduling algorithm, a deficit round-robinscheduling algorithm or any other type of scheduling algorithm capableof scheduling utilization of a limited resource, which is link 20 inthis instance.

To illustrate the generation of grant map 64, universal grant schedulerunit 24 may first access parameter table 66 to determine a totalbandwidth that can be provided via link 20. Universal grant schedulerunit 24 may then determine a service level agreement associated with afirst one of ONTs 16 by accessing SLA table 68 using what is commonlyreferred to as an allocation identifier (which is commonly referred toas an “allocID”). An allocID may uniquely identify a traffic container(which is commonly referred to as a “T-cont”) of one of ONTs 16. Asnoted above, ONTs 16 may include one or more traffic containers, such asone for voice, a second for data and a third for video. Downstreammonitoring table 52 may associate monitored data amounts 58 with PONidentifiers (IDs) in downstream table 52, where each ONT is assigned andassociated with a different PON ID. Typically, status requests are sentto each allocID, requesting the amount of data waiting at the associatedT-cont and status reports are generated that identify the amount of datawaiting at that particular T-cont for transmission upstream.

Likewise, TM DBA unit 36 may associate monitored data amounts 62 withallocIDs. Downstream monitoring unit 26, SR DBA unit 34 and TM DBA unit36 may report amounts 58, 53 and 62 respectively with their associatedallocIDs. Translator unit 38 typically stores the then converted GCPs 56to entries of GCP table 54 associated with the allocIDs. Universal grantscheduler unit 24 may maintain SLA table 68 by allocID, associating eachallocID with a defined service level agreement. Universal grantscheduler 24 may further maintain data with regard to past delivery ofservices in SLA table 68, such as an amount of data allowed to be sentupstream in a previous upstream time slot, for purposes of determiningcurrent provisioning of bandwidth via grant map 64.

Analyzing GCP table 54, universal grant scheduler unit 24 may determineallocIDs that require upstream bandwidth and then analyze SLA table 68to determine a current amount of bandwidth that should be offered toeach of the allocIDs, as well as, to ensure that maximum bandwidthlimits are enforced. Universal grant scheduler unit 24 may then schedulethe available bandwidth defined by parameter table 66 using one of theabove listed scheduling algorithms to allocate one or more GCPs 54 forassociated ones of ONTs 16 to time slots defined in grant map 64.

Upon allocating these GCPs 56, universal grant scheduler unit 24 mayupdate GCP table 54 to decrement the number of GCPs 56 stored to entriesassociated with allocIDs to reflect the grant of a time slot. Each oneof GCPs 56 corresponds to a time slot, meaning that if universal grantscheduler unit 24 scheduled three of GCPs 56 for an allocID identifyinga T-cont of ONT 16A, for example, universal grant scheduler unit 24decrements three of GCPs 56 stored to the entry associated with thatallocID. Considering that universal grant scheduler unit 24 no longerneed convert data amounts to grant cycles or time slots during thisgrant map generation time period but only assign these GCPs to timeslots within grant map 64 according to the implemented schedulingalgorithm, universal grant scheduler unit 24 may enable a number ofbenefits.

First, by utilizing pre-computed (where pre-computed is used herein torefer to the fact that GCPs may be computed without regard to the grantmap generation time period and therefore may be generally pre-computedwith respect to any given scheduling round) GCPs, universal grantscheduler unit 24 may work on much smaller number representations.Rather than perform mathematical operations with respect to potentiallylarge (in terms of number of bits) representations of the amount of datawaiting to be sent upstream at each ONT, universal grant scheduler unit24 may compute the grant map from GCPs, which represent the amount ofdata waiting to be sent upstream in a more compact form. Consideringthat computation times for mathematical operations are generallydirectly proportional to the size of the data (in terms of bits) towhich the mathematical operation is performed, reducing the size of thedata to which the mathematical operation is applied may improve thespeed with which universal grant scheduler unit 24 may perform thesemathematical operations. As a result, universal grant scheduler unit 24may perform more iterations of this mathematical operation with respectto GCPs in comparison to the actual amount of data reported ormonitored, which may improve scheduling accuracy.

Second, use of GCPs may require less storage space, as GCPs representthe amount of data waiting to be sent upstream in a more compact form.Reducing memory requirements to store this amount of data may enableuniversal grant scheduler unit 24 to implement more GPON MACs in thesame amount space as that conventionally used to implement a universalgrant scheduler. This reduction in space may also translate into reducedcost and/or more board space for other units.

Third, use of GCPs may enable universal grant scheduler unit 24 toscheduler upstream time slots regardless of the way in which these dataamounts are collected, which in effect may unify scheduling. The GCPmay, in effect, abstract data amounts from the manner in which thesedata amounts were collected so as to enable a single universal schedulerto schedule upstream time slots. For example, SR DBA reports dataamounts using the representation discussed above, while TR DBA monitorsactual amounts sent upstream and downstream monitoring monitors anamount sent downstream. All three of these values may be pertinent forperforming upstream tiem slot allocation, but all three may representtheir respective data amounts differently. This differentrepresentations require additional operations to be performed so as toenable all three to be scheduled. Rather than perform these operationsduring the grant map generation time period, the techniques facilitatethe abstraction of these representations into a single unifying oruniversal GCP representation with the added benefits discussed above. Byusing GCPs, the techniques may leverage common scheduling hardwarebetween what would have been three different scheduling implementationsto reduce overall size (in terms of board space by providing oneuniversal scheduler) and also improving performance.

Universal grant scheduler unit 24 may transmit grant map 64 downstreamover link 22 via interface 34N to ONTs 16. The process described abovemay then be repeated only an initial grant map need not be generated andsent. Instead, TM DBA unit 36 may monitor upstream data 42 sent inaccordance with grant map 64, providing monitored upstream data amounts62 to translator unit 38. In some instances, universal grant schedulerunit 24 may prepare a similar sort of initial grant map to give ONTs 16that previously had no data to send a chance to delivery data upstream.This grant map (which may be referred to as a polling grant map) may besubstantially similar to the initial grant map described above and theinitial grant map may be considered a polling grant map. In some otherinstances, rather than poll those of ONTs 16 that do not support SR DBAthrough a polling grant map, these ones of ONTs 16 may be able torequest an upstream time slot through a control channel (which in thiscontext represents a dedicated time reserved over link 22 during whichONTs 16 may communicate control, rather than payload, data to OLT 12).

FIG. 3 is a flowchart illustrating exemplary operation of an opticalline terminal, such as OLT 12 of FIG. 2, in implementing the universalgrant scheduling aspects of the techniques described in this disclosure.Initially, OLT 12 determines an amount of data waiting at ONTs 16 fordelivery upstream to OLT 12 in the manner described above (i.e., eitherusing status reporting (SR) and/or traffic monitoring (TM), in thisexample) (70). That is, control unit 30 of OLT 12 includes SR DBA unit34 and TM DBA unit 36, where SR DBA unit 34 determines an amount ofupstream data 53 waiting at ONTs 16 by sending status request 48 to andreceiving status reports 50 from ONTs 16 and TM DBA unit 36 determinesan amount of upstream data 62 waiting at ONTs 16 by monitoring upstreamdata sent during time slots allocated to those ONTs 16 via a previouslysent grant map 64.

Regardless of how upstream data amounts 53 and 62 are determined,translator unit 38 converts upstream data amounts 53 and 62 to CGPs 56in accordance with conversion formula 54, again as described above (72).Translator unit 38 may perform this translation or conversion from dataamounts 53 and 62 to corresponding GCPs 56 while still collectingamounts 53, 62 for other ONTs 16 and prior to having to generate thegrant map. Translator unit 38 may then store GCPs 56 to correspondingentries of GCP table 54 in the manner described above (74). If timeremains before the grant map needs to be generated, meaning that thecurrent scheduling round is not yet complete and it is not time togenerate the grant map (“NO” 76), SR DBA unit 34 and TM DBA unit 36 maycontinue to determine upstream data amounts 53, 62 for those active (inthe sense of being powered or otherwise activated) ones of ONTs 16.Translator unit 38 continues to convert these upstream data amounts 53,62 to GCPs 56 and store these GCPs 56 to CGP table 54 (72, 74). However,if the current scheduling round has completed and it is time to generatethe grant map (“YES” 76), universal grant scheduler unit 24 generatesgrant map 64 based on GCPs 56 stored to GCP table 54 for each active oneof ONTs 16 in the manner described above (78). In addition, universalgrant scheduler unit 24 may determine or otherwise generate grant map 64based on parameter table 66 and SLA table 68, as noted above.

While universal grant scheduler unit 24 generates grant map 64, SR DBAunit 34 and TM DBA unit 36 may continue to receive stat reports andmonitor upstream data transmission to determine upstream data amounts53, 62. Thus, while shown in the example of FIG. 3 as if SR DBA unit 34and TM DBA unit 36 stop monitoring upstream data amounts 53, 62,converting these data amounts to GCPs and storing these GCPs to the GCPtable while universal grant scheduler unit 24 generates grant map 64, SRDBA unit 34 and TM DBA unit 36 may continue to determine these dataamounts and translator unit 36 may continue convert these data amountsto GCPS and potentially store these GCPS to the GCP table whileuniversal grant scheduler unit 24 generates the grant map. In thisrespect, the techniques should not be strictly limited to the example ofFIG. 3.

In any event, after generating grant map 64, universal grant schedulerunit 24 transmits grant map 64 to ONTs 16 over link 20 via interface 32N(80). Interface 32N then receives upstream data 42 from ONTs 16 inaccordance with grant map 64 and forwards upstream data 42 to itsdestination (often over link 22 via interface 32A to a public network,such as the Internet) (82, 84). The techniques may continue in thismanner with TM DBA unit 36 monitoring this upstream data 42 while SR DBAunit 34 polls ONTs 16 for their upstream data amounts 53 by sending astatus request 48 and receiving status reports 50 in response to statusrequest 48 (70). Translator unit 36 then converts amounts 53, 62 to GCPs56, which are stored to GCP table 54 (72, 74). Universal grant schedulerunit 24 may, while SR DBA unit 34 and TM DBA unit 36 may again continueto determine these data amounts and translator unit 36 may continueconvert these data amounts to GCPS and potentially store these GCPS tothe GCP table, generate another grant map 64 based on GCPs 56 stored toGCP table 54 for each active one of ONTs 16 and transmit grant map 64.

FIG. 4 is a flowchart illustrating exemplary operation of an opticalline terminal, such as OLT 12 of FIG. 2, in implementing the downstreamtraffic monitoring aspects of the techniques described in thisdisclosure. Initially, OLT 12 determines an amount of data waiting atONTs 16 for delivery upstream to OLT 12 in the manner described above(i.e., either using status reporting (SR) and/or traffic monitoring(TM), in this example) (90). That is, control unit 30 of OLT 12 includesSR DBA unit 34 and TM DBA unit 36, where SR DBA unit 34 determines anamount of upstream data 53 waiting at ONTs 16 by sending status request48 to and receiving status reports 50 from ONTs 16 and TM DBA unit 36determines an amount of upstream data 62 waiting at ONTs 16 bymonitoring upstream data sent during time slots allocated to those ONTs16 via a previously sent grant map 64.

Regardless of how upstream data amounts 53 and 62 are determined, SR DBAunit 34 and TM DBA unit 36 store upstream data amounts 53 and 62 to GCPtable 54 after being converted, in this example to GCPs 56 in accordancewith the universal grant scheduling aspects of the techniques describedin this disclosure. While described with respect to the grant schedulingaspects of the techniques, the downstream monitoring aspects of thetechniques may be implemented separate from the grant schedulingaspects. In these instances, OLT 12 may store upstream data amounts 53,62 to a table within a grant scheduler or similar unit that may besimilar to GCP table 54 only, instead of storing GCPs, it storesupstream data amounts.

However, assuming the various aspects of the techniques are implementedin conjunction as described in the examples of this disclosure,translator unit 38 converts upstream data amounts 53 and 62 to CGPs 56in accordance with conversion formula 54, again as described above.Translator unit 38 may perform this translation or conversion from dataamounts 53 and 62 to corresponding GCPs 56 while still collectingamounts 53, 62 for other ONTs 16 and prior to determining a last amount53 or 62 for those active (in the sense of being powered or otherwiseactivated) ones of ONTs 16. Translator unit 38 may then store GCPs 56 tocorresponding entries of GCP table 54 in the manner described above. Inthis respect, translator unit 38 stores upstream data amounts 53, 62 toGCP table 54 in the form of GCPs 56 (92).

Meanwhile, downstream monitoring unit 26 determines an amount of data 58sent downstream by OLT 12 to each of active ones of ONTs 16 in themanner described above (94). Downstream monitoring unit 26 may storethese downstream data amounts 58 to corresponding entries of downstreamtable 52. Downstream monitoring unit 26 may then compare downstream dataamounts 58 to a threshold or other metric defined as one of monitoringparameters 44 (96). In some instances, rather than compare downstreamdata amounts 58, downstream monitoring unit 26 may determine a change indownstream data amounts over any given period of time, where the periodof time may be configurable or pre-defined. Downstream monitoring unit26 may then compare this change in downstream data amounts to thethreshold or other metric defined as one of monitoring parameters 44.

In any event, if one or more of downstream data amounts 58 or changes indownstream data amounts (which effectively represents a change in thedownstream rate of data delivery) exceeds the threshold (“YES” 98),downstream monitoring unit 26 may forward this downstream data amount 58to translation unit 36, which translates downstream data amounts 58 toone or more GCPs 56. Translation unit 36 then updates an entry of GCPtable 54 corresponding to the one of ONTs 16 for which downstream dataamount 58 was monitored to increase the number of GCPs 56 assigned tothat one of ONTs 16. In this manner, OLT 12 updates an amount ofupstream data based on the monitored amount of downstream data (100).Again, while described in this example with respect to GCPs, thedownstream monitoring aspects of the techniques set forth in thisdisclosure may be implemented with respect to data amounts rather thanGCPs to potentially reduce latency when implementing conventional orstandard grant scheduling algorithms.

If one or more downstream data amounts 58 do (or changes in thedownstream data rate of delivery does) not exceed the threshold (“NO”98) or after updating GCPs 56 stored to GCP table 54 based on downstreamdata amounts 58, universal grant scheduler unit 24 may generate grantmap 64 based on GCPs 56 stored to GCP table 54 for each active one ofONTs 16 (102). In addition, universal grant scheduler unit 24 maydetermine or otherwise generate grant map 64 based on parameter table 66and SLA table 68, as noted above. After generating grant map 64,universal grant scheduler unit 24 transmits grant map 64 to ONTs 16 overlink 20 via interface 32N (104). Interface 32N then receives upstreamdata 42 from ONTs 16 in accordance with grant map 64 and forwardsupstream data 42 to its destination (often over link 22 via interface32A to a public network, such as the Internet) (106, 108). Thetechniques may continue in this manner until such time that OLT 12 is nolonger active, powered or otherwise enabled or operational (90-108).

In this way, OLT 12 determines an amount of upstream data that iswaiting at one of ONTs 16 to be transmitted upstream to OLT 12 and thendetermines an amount of downstream data that is transmitted by the OLTto the one of ONTs 16. OLT 12 then increases the determined amount ofupstream data based on the determined amount of downstream data istransmitted by OLT 12 to the one of ONTs 16 and, after increasing thedetermined amount of upstream data, generates an upstream grant map 64that grants time slots to the one or more of ONTs 16 based on the amountof upstream data determined for each ONTs 16.

OLT 12 then transmits the upstream grant map downstream to ONTs 16,receives upstream data in accordance with upstream grant map andforwards this upstream traffic to its intended destination. Bymonitoring downstream data amounts and then increasing upstream dataamounts based on the monitored downstream amounts, OLT 12 mayproactively assign upstream bandwidth to those of ONTs 16 that arelikely to require this bandwidth to response to TCP or other windowingprotocols that limit the amount of data that can be sent. By proactivelyassigning this upstream bandwidth, OLT 12 may reduce or, in someinstances, prevent bandwidth allocation thrashing whereby both OLT 12and the underlying protocol each misidentify the reason why ONTs 16 failto fully utilize their allotted bandwidth and then decrease bandwidth atodds with one another.

The techniques described herein may be implemented in hardware,firmware, or any combination thereof. The hardware may, in someinstances, also execute software. Any features described as modules,units or components may be implemented together in an integrated logicdevice or separately as discrete but interoperable logic devices. Insome cases, various features may be implemented as an integrated circuitdevice, such as an integrated circuit chip or chipset. If implemented insoftware, the techniques may be realized at least in part by acomputer-readable medium comprising instructions that, when executed,cause a processor to perform one or more of the methods described above.

A computer-readable medium may form part of a computer program product,which may include packaging materials. A computer-readable medium maycomprise a computer data storage medium such as random access memory(RAM), synchronous dynamic random access memory (SDRAM), read-onlymemory (ROM), non-volatile random access memory (NVRAM), electricallyerasable programmable read-only memory (EEPROM), FLASH memory, magneticor optical data storage media, and the like, including non-transitorycomputer-readable mediums. The techniques additionally, oralternatively, may be realized at least in part by a transitorycomputer-readable communication medium that carries or communicates codein the form of instructions or data structures and that can be accessed,read, and/or executed by a computer.

The code or instructions may be executed by one or more processors, suchas one or more DSPs, general purpose microprocessors, ASICs, fieldprogrammable logic arrays (FPGAs), or other equivalent integrated ordiscrete logic circuitry. Accordingly, the term “processor,” as usedherein may refer to any of the foregoing structure or any otherstructure suitable for implementation of the techniques describedherein. In addition, in some aspects, the functionality described hereinmay be provided within dedicated software modules or hardware modules.The disclosure also contemplates any of a variety of integrated circuitdevices that include circuitry to implement one or more of thetechniques described in this disclosure. Such circuitry may be providedin a single integrated circuit chip or in multiple, interoperableintegrated circuit chips in a so-called chipset. Such integrated circuitdevices may be used in a variety of applications.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A method comprising: determining, with an optical line terminal (OLT)coupled to a plurality of optical network terminals (ONTs) thatfacilitate the transfer of data between a corresponding one of aplurality of customer network devices and the OLT, an amount of upstreamdata that is waiting at one of the plurality of ONTs to be transmittedupstream to the OLT; determining, with the OLT, an amount of downstreamdata that is transmitted by the OLT to the one of the plurality of ONTs;increasing the determined amount of upstream data based on thedetermined amount of downstream data that is transmitted by the OLT tothe one of the plurality of ONTs; after increasing the determined amountof upstream data, generating an upstream grant map that grants timeslots to the one or more of the plurality of ONTs based on the amount ofupstream data determined for each of the plurality of ONTs; andtransmitting, with the OLT, the upstream grant map downstream to theplurality of ONTs.
 2. The method of claim 1, further comprisingdetermining a change in the amount of downstream data that istransmitted by the OLT to the first one of the plurality of ONTs basedon the determined amount of downstream data, wherein increasing thedetermined amount of upstream data comprises increasing the determinedamount of upstream data based on the determined change in the amount ofdownstream data.
 3. The method of claim 1, wherein the downstream datacomprises data sent downstream in accordance with a protocol able toreduce bandwidth usage.
 4. The method of claim 3, wherein the protocolcomprises a transmission control protocol (TCP) that is able to reducebandwidth usage using a windowing mechanism.
 5. The method of claim 1,further comprising comparing the determined amount of downstream data toa threshold, wherein increasing the determined amount of upstream datacomprises, based on the comparison, increasing the determined amount ofupstream data based on the determined amount of downstream data that istransmitted by the OLT to the one of the plurality of ONTs prior togranting the time slots.
 6. The method of claim 1, further comprising,prior to determining an amount of upstream data that is waiting at aanother one of the plurality of ONTs different from the one of theplurality of ONTs to be transmitted upstream to the OLT and prior togranting time slots to one or more of the plurality of ONTs, computing anumber of grant cycles pending (GCPs) with the OLT based on thedetermined amount of data that is waiting at the one of a plurality ofONTs to be transmitted upstream to the OLT, and wherein generating thegrant map comprises, after computing a number of GCPs for each of theplurality of ONTs based on a determined amount of data that is waitingto be transmitted upstream to the OLT for each of the plurality of ONTs,generating the grant map to grant the time slots to the one or more ofthe plurality of ONTs based on the number of GCPs computed for each ofthe plurality of ONTs.
 7. The method of claim 1, further comprising:receiving upstream data from each of the plurality of ONTs in accordancewith the transmitted grant map; and forwarding the upstream data to anintended destination specified by the upstream data.
 8. The method ofclaim 1, wherein determining an amount of upstream data that is waitingat one of the plurality of ONTs to be transmitted upstream to the OLTcomprises: transmitting a status request to the plurality of ONTs;receiving a status report from the first one of the plurality of ONTs,wherein the status report defines either an exact or an approximateamount of upstream data that is waiting at the first one of theplurality of ONTs to be transmitted upstream to the OLT, and determiningthe amount of upstream data that is waiting at the first one of theplurality of ONTs to be transmitted upstream to the OLT based on theexact or approximate amount of upstream data defined by the receivedstatus report.
 9. The method of claim 1, wherein determining an amountof upstream data that is waiting at the one of the plurality of ONTs tobe transmitted upstream to the OLT comprises: determining an amount ofdata sent upstream by the first one of the OLTs in response to apreviously sent grant map granting at least one time slot for a previousperiod of time during which the first one of the OLTs was to communicatedata upstream; and determining the amount of upstream data that iswaiting at the first one of the plurality of ONTs to be transmittedupstream to the OLT based on the determined amount of data sent upstreamby the first one of the OLTs in response to the previously sent grantmap.
 10. The method of claim 1, wherein the plurality of ONTs couple tothe OLT via a link that is shared by two or more of the ONTs, whereinthe ONTs and the OLT reside in a passive optical network (PON), andwherein the link that is shared by the two or more of the ONTs comprisesan optical fiber link.
 11. An optical line terminal (OLT) coupled to aplurality of optical network terminals (ONTs) that facilitate thetransfer of data between a corresponding one of a plurality of customernetwork devices and the OLT, the OLT comprising: a control unit thatdetermines an amount of upstream data that is waiting at one of theplurality of ONTs to be transmitted upstream to the OLT, determines anamount of downstream data that is transmitted by the OLT to the one ofthe plurality of ONTs, increases the determined amount of upstream databased on the determined amount of downstream data transmitted by the OLTto the one of the plurality of ONTs and after increasing the determinedamount of upstream data, generates an upstream grant map that grantstime slots to the one or more of the plurality of ONTs based on theamount of upstream data determined for each of the plurality of ONTs;and at least one interface that transmits the upstream grant mapdownstream to the plurality of ONTs.
 12. The OLT of claim 11, whereinthe control unit further determines a change in the amount of downstreamdata that is transmitted by the OLT to the first one of the plurality ofONTs based on the determined amount of downstream data and increases thedetermined amount of upstream data based on the determined change in theamount of downstream data.
 13. The OLT of claim 11, wherein thedownstream data comprises data sent downstream in accordance with aprotocol able to reduce bandwidth usage.
 14. The OLT of claim 13,wherein the protocol comprises a transmission control protocol (TCP)that is able to reduce bandwidth usage using a windowing mechanism. 15.The OLT of claim 11, wherein the control unit further compares thedetermined amount of downstream data to a threshold and, based on thecomparison, increases the determined amount of upstream data based onthe determined amount of downstream data that is transmitted by the OLTto the one of the plurality of ONTs prior to granting the time slots.16. The OLT of claim 11, wherein the control unit further, prior todetermining an amount of upstream data that is waiting at a another oneof the plurality of ONTs different from the one of the plurality of ONTsto be transmitted upstream to the OLT and prior to granting time slotsto one or more of the plurality of ONTs, computes a number of grantcycles pending (GCPs) based on the determined amount of data that iswaiting at the one of a plurality of ONTs to be transmitted upstream tothe OLT and, after computing a number of GCPs for each of the pluralityof ONTs based on a determined amount of data that is waiting to betransmitted upstream to the OLT for each of the plurality of ONTs,generates the grant map to grant the time slots to the one or more ofthe plurality of ONTs based on the number of GCPs computed for each ofthe plurality of ONTs.
 17. The OLT of claim 11, wherein the at least oneinterface further receives upstream data from each of the plurality ofONTs in accordance with the transmitted grant map and forwards theupstream data to an intended destination specified by the upstream data.18. The OLT of claim 11, wherein the at least one interface furthertransmits a status request to the plurality of ONTs, and receives astatus report from the first one of the plurality of ONTs, wherein thestatus report defines either an exact or an approximate amount ofupstream data that is waiting at the first one of the plurality of ONTsto be transmitted upstream to the OLT, and wherein the control unitfurther determines the amount of upstream data that is waiting at thefirst one of the plurality of ONTs to be transmitted upstream to the OLTbased on the exact or approximate amount of upstream data defined by thereceived status report.
 19. The OLT of claim 11, wherein the controlunit further determines an amount of data sent upstream by the first oneof the OLTs in response to a previously sent grant map granting at leastone time slot for a previous period of time during which the first oneof the OLTs was to communicate data upstream and determines the amountof upstream data that is waiting at the first one of the plurality ofONTs to be transmitted upstream to the OLT based on the determinedamount of data sent upstream by the first one of the OLTs in response tothe previously sent grant map.
 20. The OLT of claim 11, wherein theplurality of ONTs couple to the OLT via a link that is shared by two ormore of the ONTs, wherein the ONTs and the OLT reside in a passiveoptical network (PON), and wherein the link that is shared by the two ormore of the ONTs comprises an optical fiber link.
 21. The OLT of claim11, wherein the control unit comprises a field programmable gate array.22. A network system comprising: a plurality of customer networkdevices; and a passive optical network (PON) comprising: an optical lineterminal (OLT); and a plurality of optical network terminals (ONTs) thatfacilitate the transfer of data between a corresponding one of theplurality of customer network devices and the OLT, wherein the OLTcomprises: a control unit that determines an amount of upstream datathat is waiting at one of the plurality of ONTs to be transmittedupstream to the OLT, determines an amount of downstream data that istransmitted by the OLT to the one of the plurality of ONTs, increasesthe determined amount of upstream data based on the determined amount ofdownstream data transmitted by the OLT to the one of the plurality ofONTs and, after increasing the determined amount of upstream data,generates an upstream grant map that grants time slots to the one ormore of the plurality of ONTs based on the amount of upstream datadetermined for each of the plurality of ONTs; and at least one interfacethat transmits the upstream grant map downstream to the plurality ofONTs.
 23. The network system of claim 22, wherein the control unitfurther determines a change in the amount of downstream data that istransmitted by the OLT to the first one of the plurality of ONTs basedon the determined amount of downstream data and increases the determinedamount of upstream data based on the determined change in the amount ofdownstream data.
 24. The network system of claim 22, wherein thedownstream data comprises data sent downstream in accordance with aprotocol able to reduce bandwidth usage.
 25. The network system of claim24, wherein the protocol comprises a transmission control protocol (TCP)that is able to reduce bandwidth usage using a windowing mechanism. 26.The network system of claim 22, wherein the control unit furthercompares the determined amount of downstream data to a threshold and,based on the comparison, increases the determined amount of upstreamdata based on the determined amount of downstream data that istransmitted by the OLT to the one of the plurality of ONTs prior togranting the time slots.
 27. The network system of claim 22, wherein thecontrol unit further, prior to determining an amount of upstream datathat is waiting at a another one of the plurality of ONTs different fromthe one of the plurality of ONTs to be transmitted upstream to the OLTand prior to granting time slots to one or more of the plurality ofONTs, computes a number of grant cycles pending (GCPs) based on thedetermined amount of data that is waiting at the one of a plurality ofONTs to be transmitted upstream to the OLT and, after computing a numberof GCPs for each of the plurality of ONTs based on a determined amountof data that is waiting to be transmitted upstream to the OLT for eachof the plurality of ONTs, generates the grant map to grant the timeslots to the one or more of the plurality of ONTs based on the number ofGCPs computed for each of the plurality of ONTs.
 28. The network systemof claim 22, wherein the at least one interface further receivesupstream data from each of the plurality of ONTs in accordance with thetransmitted grant map and forwards the upstream data to an intendeddestination specified by the upstream data.
 29. The network system ofclaim 22, wherein the at least one interface further transmits a statusrequest to the plurality of ONTs, and receives a status report from thefirst one of the plurality of ONTs, wherein the status report defineseither an exact or an approximate amount of upstream data that iswaiting at the first one of the plurality of ONTs to be transmittedupstream to the OLT, and wherein the control unit further determines theamount of upstream data that is waiting at the first one of theplurality of ONTs to be transmitted upstream to the OLT based on theexact or approximate amount of upstream data defined by the receivedstatus report.
 30. The network system of claim 22, wherein the controlunit further determines an amount of data sent upstream by the first oneof the OLTs in response to a previously sent grant map granting at leastone time slot for a previous period of time during which the first oneof the OLTs was to communicate data upstream and determines the amountof upstream data that is waiting at the first one of the plurality ofONTs to be transmitted upstream to the OLT based on the determinedamount of data sent upstream by the first one of the OLTs in response tothe previously sent grant map.
 31. The network system of claim 22,wherein the plurality of ONTs couple to the OLT via a link that isshared by two or more of the ONTs, wherein the ONTs and the OLT residein a passive optical network (PON), and wherein the link that is sharedby the two or more of the ONTs comprises an optical fiber link.
 32. Thenetwork system of claim 22, wherein the control unit comprises a fieldprogrammable gate array.
 33. A non-transitory computer-readable mediumcomprising instructions that, when executed, cause one or moreprocessors to: determine, with an optical line terminal (OLT) coupled toa plurality of optical network terminals (ONTs) that facilitate thetransfer of data between a corresponding one of a plurality of customernetwork devices and the OLT, an amount of upstream data that is waitingat one of the plurality of ONTs to be transmitted upstream to the OLT;determine, with the OLT, an amount of downstream data that istransmitted by the OLT to the one of the plurality of ONTs; increase thedetermined amount of upstream data based on the determined amount ofdownstream data transmitted by the OLT to the one of the plurality ofONTs; after increasing the determined amount of upstream data, generatean upstream grant map that grants time slots to the one or more of theplurality of ONTs based on the amount of upstream data determined foreach of the plurality of ONTs; and transmit, with the OLT, the upstreamgrant map downstream to the plurality of ONTs.
 34. The non-transitorycomputer-readable medium of claim 33, further comprising instructionsthat, when executed, cause the one or more processors to: determine achange in the amount of downstream data that is transmitted by the OLTto the first one of the plurality of ONTs based on the determined amountof downstream data; and increase the determined amount of upstream databased on the determined change in the amount of downstream data.
 35. Thenon-transitory computer-readable medium of claim 33, wherein thedownstream data comprises data sent downstream in accordance with aprotocol able to reduce bandwidth usage.
 36. The non-transitorycomputer-readable medium of claim 35, wherein the protocol comprises atransmission control protocol (TCP) that is able to reduce bandwidthusage using a windowing mechanism.
 37. The non-transitorycomputer-readable medium of claim 33, further comprising instructionsthat, when executed, cause the one or more processors to: compare thedetermined amount of downstream data to a threshold; based on thecomparison, increase the determined amount of upstream data based on thedetermined amount of downstream data that is transmitted by the OLT tothe one of the plurality of ONTs prior to granting the time slots. 38.The non-transitory computer-readable medium of claim 33, furthercomprising instructions that, when executed, cause the one or moreprocessors to: prior to determining an amount of upstream data that iswaiting at a another one of the plurality of ONTs different from the oneof the plurality of ONTs to be transmitted upstream to the OLT and priorto granting time slots to one or more of the plurality of ONTs, computea number of grant cycles pending (GCPs) with the OLT based on thedetermined amount of data that is waiting at the one of a plurality ofONTs to be transmitted upstream to the OLT; and after computing a numberof GCPs for each of the plurality of ONTs based on a determined amountof data that is waiting to be transmitted upstream to the OLT for eachof the plurality of ONTs, generate the grant map to grant the time slotsto the one or more of the plurality of ONTs based on the number of GCPscomputed for each of the plurality of ONTs.
 39. The non-transitorycomputer-readable medium of claim 33, further comprising instructionsthat, when executed, cause the one or more processors to: receiveupstream data from each of the plurality of ONTs in accordance with thetransmitted grant map; and forward the upstream data to an intendeddestination specified by the upstream data.
 40. The non-transitorycomputer-readable medium of claim 33, further comprising instructionsthat, when executed, cause the one or more processors to: transmit astatus request to the plurality of ONTs; receive a status report fromthe first one of the plurality of ONTs, wherein the status reportdefines either an exact or an approximate amount of upstream data thatis waiting at the first one of the plurality of ONTs to be transmittedupstream to the OLT, and determine the amount of upstream data that iswaiting at the first one of the plurality of ONTs to be transmittedupstream to the OLT based on the exact or approximate amount of upstreamdata defined by the received status report.
 41. The non-transitorycomputer-readable medium of claim 33, further comprising instructionsthat, when executed, cause the one or more processors to: determine anamount of data sent upstream by the first one of the OLTs in response toa previously sent grant map granting at least one time slot for aprevious period of time during which the first one of the OLTs was tocommunicate data upstream; and determine the amount of upstream datathat is waiting at the first one of the plurality of ONTs to betransmitted upstream to the OLT based on the determined amount of datasent upstream by the first one of the OLTs in response to the previouslysent grant map.
 42. The non-transitory computer-readable medium of claim33, wherein the plurality of ONTs couple to the OLT via a link that isshared by two or more of the ONTs, wherein the ONTs and the OLT residein a passive optical network (PON), and wherein the link that is sharedby the two or more of the ONTs comprises an optical fiber link.